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Compact Base64-first Database-friendly UIDs

Published on 2023-12-30. Last updated on 2025-05-22

Compact
20 characters encode 120 bits of payload.

Efficient
Speedy encoding and decoding.

Compatible
Can be used in URLs, form-fields and as HTML attributes.

Lexicographically ordered
The bitstring and the encoded string sort the same.

Database-friendly
Time-prefix improves database locality and performance.

Structure of a BaseUid

A BaseUid consist of two parts:

  1. 48bits of POSIX time in nanoseconds, left-shifted by 2 bits1
  2. 72bits of randomness


These two parts are concatenated into a 120bit long bitstring:

         8      16      24      32      40      48      56      64      72      80      88      96      104     112     120
┏━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┓
┃               time (00-47)                    ┆                               rnd (48-119)                            ┃
┗━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┛


The bitstring is encoded as an ASCII string using the lexicographically-ordered Base64 alphabet -0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz.

This produces an ASCII string of 20 characters, of which 8 characters represent the time-component and 12 characters represent the randomness-component.

Example

A BaseUid from the start of 2022 could be ANjssJkyfa3H00J9ZPJG.
ANjssJky is the timestamp-component for 2022-01-01T00:00:00Z and fa3H00J9ZPJG is the randomness-component that differs with each generated value, even if the point in time stays the same.

Conversion to UUIDv8 Format

BaseUids can easily be converted into UUIDv8 format if required:

         8      16      24      32      40      48      56      64      72      80      88      96      104     112     120     128
┏━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┳━┯━┯━┯━┓
┃               time (00-47)                    ┆VER┆rnd (52-63)┆V┆             rnd (66-125)                                  ┆Z┃
┗━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┻━┷━┷━┷━┛
                                                 ^               ^                                                             ^
                                                 |               |                                                             |
                                              ┌VER (constant)┐  ┌VAR (constant)┐                                   ┌Z (constant)┐
                                              │ 1 0 0 0      │  │ 1 0          │                                   │ 0 0        │
                                              └──────────────┘  └──────────────┘                                   └────────────┘

Implementations

Comparison with other UID formats

  Payload Compact Efficient Compatible Ordered Database-friendly
BaseUID 120bits ✔ Base64 ✔ ✔ ✔ ✔
UUID text repr. 128bits ✖ Base16 ✔ ✖ ✔ ✖
ULID 128bits 🞈 Base32 🞈 ✖ ✔ ✔
LexicalUUID 128bits ✖ Base16 ✖ ✖ ✔ ✔
Flake 128bits ✔ Base62 ✖ ✖ ❔ ✔
ShardingID 64bits ✖ Base10 🞈 ✖ ✔ ✔
KSUID 160bits ✔ Base62 ✖ ✖ ✔ ✔
Elasticflake 120bits ✔ Base64 ✔ ✖ ✖ ✔
FlakeID 64bits ✖ Base10/16 ✔ ✖ ✔ ✔
Sonyflake 63bits ✖ Base10 ✔ ✖ ✔ ✔
orderedUuid 120bits ✖ Base10 ✔ ✖ ✖ ✔
COMBGUID 120bits ✖ Base10 ✔ ✖ ✖ ✔
SID 128bits ✔ Base10/16/32/64 ✔ ✖ ✔ ✔
pushID 120bits ✔ Base64 ✔ ✖ ✔ ✔
XID 96bits 🞈 Base32 ✔ ✖ ✔ ✔
ObjectID 96bits ✖ Base16 ✔ ✖ ✔ ✔
CUID 128bits ✖ Base36 ✖ ✔ ✖ ✔
TypeID 128bits 🞈 Base32 ✖ ✔ ✔ ✔

  1. This selection ensures that the resulting Base64-encoded string starts with a letter for timestamps between the years 2021 and 2260. This allows the use of BaseUids without escaping or additional effort in places that do not allow values starting with a digit (such as HTML attributes values, which are required to be valid CSS identifiers). ↩